1. Field of the Invention
The present invention relates to a thin film forming apparatus and thin film forming method used for a deposition process in manufacturing, for example, a semiconductor, a magnetic recording medium, a solar cell, or a liquid crystal display, and a shield component which can be used for the thin film forming apparatus.
2. Description of the Related Art
A thin film forming apparatus used in producing a product such as a semiconductor or a magnetic recording medium is intended to deposit a thin film, such as a metal film, on a substrate, such as a silicon wafer.
However, at the same time, this thin film is also deposited on various portions inside the apparatus, other than the target substrate. This deposited thin film will be called an adherent film hereinafter. The thickness of the adherent film increases as production is continued and deposition on a substrate is performed an increasing number of times. When the thickness of the adherent film exceeds a certain threshold, the adherent film peels off the surface, on which it has been deposited, due to a stress acting on itself. If the adherent film peels off during production, that is, during deposition on the substrate, the atmosphere in the apparatus changes. Because the thin film deposited on the substrate on this occasion contains particles originating from the adherent film, the reproducible film quality expected of the deposited film cannot be obtained. In, for example, a sputtering apparatus, when peel-off of an adherent film occurs during deposition, the plasma discharge conditions used in the sputtering process change, and the quality of the deposited film, in turn, changes.
Also, when peel-off of an adherent film occurs during the period in which the substrate is unloaded from the apparatus upon completion of deposition, if the next substrate is loaded into the apparatus, and deposition starts again, a particle often adheres onto the substrate surface or the substrate support table, thus making it impossible to obtain a given film quality. Depending on the deposition method, deposition itself may become impossible, posing a significant disadvantage. In, for example, a sputtering apparatus, the peeled, adherent film may change the electrical circuit characteristics of the apparatus. In such a case, unless the production in progress is stopped, the interior of the apparatus is cleaned and the peeled, adherent film is removed, plasma discharge cannot take place and production may become impossible.
To avoid these disadvantages, thin film forming apparatuses widely adopt a technique of having a built-in structure called a shield to protect the portions to which an adherent film must not adhere and periodically replacing the shield with a new one before the adherent film adhered to the shield becomes so thick as to peel off.
In putting a thin film forming apparatus into operation, an effort is made to minimize the number of times the shield needs to be replaced. That is, it is advantageous in putting the apparatus into operation to set a long shield maintenance cycle because this makes it possible to prolong the production time and save the cost required for shield replacement and cleaning in preparation for recycling.
Hence, it is common practice to process a shield to make it hard for an adherent film to peel off. For example, the shield surface is intentionally processed to have a three-dimensional pattern, for example by roughening it by blasting or spraying it with another material such as aluminum or titanium. With these types of processing, the adhesiveness of the adherent film adhering on the shield surface is improved to make it hard for the adherent film to peel off.
The same effect is known to be produced by shaping a shield such that its opening edge has a curvature equal to or larger than a predetermined threshold. For example, Mukai et al. point out in Japanese Patent Laid-Open No. 06-145976 (patent reference 1) that the amount of adhering particles per 5-inch wafer was reduced when the radius of curvature of the opening edge of a dark space shield used in the vicinity of a target for a magnetron sputtering apparatus used for an aluminum thin film was set to 3 mm or more. Similarly, Nishiwaki et al. point out in Japanese Patent Laid-Open No. 05-121358 (patent reference 2) advantages in setting the curvatures of the shield end face and corner to 1 mm to 10 mm in a sputtering apparatus used for a refractory metal film, and Ikeda et al. point out in Japanese Patent Laid-Open No. 2001-073115 (patent reference 3) advantages in setting the radii of curvature of the shield opening edge and bent portion to 0.3 mm or more in a carbon sputtering apparatus.
The shield shape includes a flat surface and a corner or curved surface. Hence, patent references 1, 2, and 3 disclose that a shield is desirably designed to have a corner or curved surface with a large radius of curvature in a region in which a change from the flat surface to the corner or curved surface takes place, or conversely, that from the corner or curved surface to the flat surface takes place.
However, a shield having a curved surface with a large radius of curvature inevitably has a large overall size. On the other hand, to place a shield in a deposition apparatus, the shield cannot be unlimitedly large and must have a size that falls within a predetermined limit. Also, as the overall shield size increases, the number of members used naturally increases, so the shield weight gets heavier. This causes difficulties in handling in terms of design associated with a method of disposing the shield, and raises the cost of the shield.
Moreover, desired deposition becomes impossible due to the occurrence of design and process constraints. When, for example, a deposition apparatus which performs deposition by sputtering that uses plasma discharge adopts a shield with a large radius of curvature, the plasma discharge space becomes narrower than when it adopts a shield with a small radius of curvature, and the characteristics and properties of the plasma itself change considerably, so a film quality reproducibility expected of the film deposited on the substrate cannot be obtained. More specifically, in that case, because the distance between the target and the shield shortens, the film thickness distribution within the plane of the film which is deposited on the substrate at a position farther than the shield when viewed from the target deteriorates.